1. Field of the Invention
This invention relates to an ultrasonic welding method for molded resin materials, wherein an upper shell half and a lower shell half of a magnetic disk cartridge, or the like, are joined to each other with an ultrasonic welding process during the processes for manufacturing the magnetic disk cartridge, or the like. This invention also relates to an apparatus for carrying out the ultrasonic welding method for molded resin materials.
2. Description of the Prior Art
Magnetic disk cartridges, each of which comprises an upper shell half, a lower shell half, and a magnetic disk housed in a shell constituted of the upper shell half and the lower shell half, are widely used as signal recording media for recording various signals. During the processes for manufacturing the magnetic disk cartridge, the magnetic disk is placed on the lower shell half, and the upper shell half is superposed upon the lower shell half. In this state, the upper shell half and the lower shell half are joined to each other with an ultrasonic welding process.
An apparatus for carrying out the ultrasonic welding process has been disclosed in, for example, Japanese Unexamined Utility Model Publication No. 1(1989)-127825. The disclosed apparatus comprises a fixed receiving section, on which an upper shell half and a lower shell half having been combined with each other are placed, and a welding horn. The welding horn moves down to the position, at which the upper shell half and the lower shell half having been combined with each other are placed on the receiving section. The welding horn holds the upper shell half and the lower shell half on the receiving section, and generates ultrasonic waves.
With the ultrasonic welding process, welding effects are determined by the amplitude of vibration at the leading end of the welding horn, the pressure applied by the welding horn onto the upper shell half and the lower shell half, and the time, for which the ultrasonic waves are applied to the upper shell half and the lower shell half. Of these three factors, the amplitude of vibration and the time, for which the ultrasonic waves are applied to the upper shell half and the lower shell half, can be set accurately.
However, the thicknesses of upper shell halves and lower shell halves vary depending on a small difference in the shape between cavities of a mold of a molding machine, or on a small difference in the shape between the molds. Therefore, a small difference occurs in the thickness between a plurality of upper shell halves and a plurality of lower shell halves, which have been molded with the molding machine. In such cases, with the conventional apparatus for carrying out the ultrasonic welding process, the pressure applied by the welding horn onto the upper shell half and the lower shell half varies for different combinations of upper shell halves and lower shell halves or for different parts of a single combination of an upper shell half and a lower shell half.
As a result, the welding effects on the upper shell half and the lower shell half vary for different combinations of upper shell halves and lower shell halves or for different welded parts of a single combination of an upper shell half and a lower shell half. Accordingly, the upper shell half and the lower shell half cannot be accurately joined to each other.